Cytosolic actin isoforms form networks with different rheological properties that indicate specific biological function

The implications of the existence of different actins expressed in epithelial cells for network mechanics and dynamics is investigated by microrheology and confocal imaging. γ-actin predominately found in the apical cortex forms stiffer networks compared to β-actin, which is preferentially organized in stress fibers. We attribute this to selective interactions with Mg2+-ions interconnecting the filaments’ N-termini. Bundling propensity of the isoforms is different in the presence of Mg2+-ions, while crosslinkers such as α-actinin, fascin, and heavy meromyosin alter the mechanical response independent of the isoform. In the presence of myosin, β-actin networks show a large number of small contraction foci, while γ-actin displays larger but fewer foci indicative of a stronger interaction with myosin motors. We infer that subtle changes in the amino acid sequence of actin isoforms lead to alterations of the mechanical properties on the network level with potential implications for specific biological functions.


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We chose sample sizes to yield sufficient numbers of counts, based on standards of the field.No size calculation was performed.
All data were included, only unsuccessful preparations of actin networks being omitted from the analysis.
To confirm the data's reproducibility, multiple researchers conducted experiments using various sample preparations on different days, incorporating additional technical replicates and preparing samples from multiple different batches of protein monomers.Inclusion of replicated data was unbiased in regards to previous results.
Not applicable for our experimental design as reconstituted networks were prepared from multiple independent preparations by multiple researchers (3) and from multiple batches of protein monomers.This is standard in the field of biophysics with reconstituted systems.The precise number of preparations is given in the supplementary information.We could use standard regression analysis to obtain unbiased results.
Blinding was unnecessary as there is no potential for bias in our measurements and data analysis.